Mechanism of Energy Coupling between Catalysis (ATP Synthesis and Hydrolysis) and H^+ Transport in ATP Synthase

三磷酸腺苷合成酶(FoF1，H^ATPase)催化水解与质子转运偶联的三磷酸腺苷合成。大肠杆菌酶与线粒体或叶绿体类囊体内膜中发现的酶相似，对了解这种复杂的酶有很大的贡献。该酶的催化部位位于膜外源F1区的β亚基或α亚基和β亚基的交界处。质子途径是由膜固有Fo扇区的a、b和c亚单位形成的。在功能上和结构上需要F1的伽马、β和epsilon亚基来将催化亚基连接到Fo扇区。通过对E.Coli酶的突变分析，确定了β亚基的催化部位和γ亚基在化学(ATP合成/水解)和渗透反应(质子转移)之间能量耦合中的活性作用(S)。对β亚基催化位点的研究结果表明：(1)富含甘氨酸的序列(Cly-Cly-Ala-Cly-Cly-Ala-Cly-Val-Cly-Lys-Thr，第149-156位)中的BetaLys-155和BetaThr-156是催化所必需的；(2)GER保守序列中的BetaClu 181和BetaArg-182是必需的催化残基；(3)BetaCly-149与BetaCly-172、BetaSer-174、BetaClu-192和BetaVal-198相近。根据这些结果，提出了与突变酶的抑制剂敏感性相一致的催化部位模型。这一模型与从F1的最新X射线结构得到的模型是一致的。遗传学研究表明，Gamma亚基在调节能量耦合(催化和质子转运之间的耦合)中起作用：GammaMet-23、GammaArg-242以及GammaCln-269和GammaVal-280之间的区域相互靠近，相互作用，从而实现有效的能量耦合。

The ATP synthase (FoFl, H^+ATPase) catalyzes ATP synthesis of hydrolysis coupling with proton translocation. Escherichia coli enzyme is similar to those found in inner mitochondrial or chloroplast thylakoid membranes, and has contributed greatly to the understanding of this complicated enzyme. The ctalytic site of the enzyme is in the beta subunit or at the interface between the alpha and beta subunits of the membrane extrinsic Fl sector. The proton pathway is fomed from the a b, and c subunit of the membrane intrinsic Fo sector. The gamma, delta, and epsilon subunits of the Fl are required funcionally and structrually to connect the catalyic subunits to the Fo sector. The mechanism of ATP hydrolysis can be studied using purified (Fl-ATPase).In this project we defined, by mutational analysis of the E.Coli enzyme, the catalytic site in the beta subunit and the active role (s) of the gamma subunit in the energy coupling between the chemical (ATP synthesis/hydrolysis) and osmotic reaction (proton translocation).Results obtained for the beta subunit catalytic site were : (1) betaLys-155 and betaThr-156 in the glycine-rich sequence (Cly-Cly-Ala-Cly-Val-Cly-Lys-Thr, residues 149-156) are essential for catalysis ;(2) betaClu 181 and betaArg-182 in the conserved GER sequence are essential catalytic residues ;(3) betaCly-149 is close to betaCly-172, betaSer-174, betaClu-192 and betaVal-198. From these results, amodel of the catalytic site is proposed that is consistent with the inhibitor sensitvities of the mutant enzmes. This model is consistent with that obtained from recent X ray structure of Fl. Genetic studies suggested that the gamma subunit plays a role in regulation energy coupling (coupling between catalysis and proton transport) : gammaMet-23, gammaArg-242, and the region between gammaCln-269 and gammaVal-280 are close to each other and interract for efficient energy coupling.